The present invention relates to sputtering targets, such as tantalum and tantalum alloy-sputtering targets, and methods to make the same.
In the sputter application field, a sputtering target assembly typically includes a sputter target and a backing plate. For instance, a metal target or metal target blank (e.g., tantalum, titanium, aluminum, copper, cobalt, tungsten, hafnium, and the like) is bonded onto a backing plate. The backing plate can be, for example, a backing plate flange assembly such as copper, aluminum, or alloys thereof. Among the factors that can affect sputtering performance of a given sputtering target assembly is the grain size and crystallographic orientation of the grains relative to the sputtering plane. The desired grain size and crystallographic texture are simultaneously achieved by using a combination of mechanical deformation and annealing.
Previous methods for forming the desired metallurgical structure in tantalum, for instance, has included mechanical deformation by forging, rolling, extrusion, and combinations thereof. Previous methods of forming tantalum sputtering targets relied upon multiple annealing steps between the mechanical deformation steps to recrystallize the grains to produce a uniform fine grain microstructure with either the (111) or (100) crystallographic planes parallel to the sputtering target plane.
For example, Michaluk et al., U.S. Pat. No. 6,348,113, describes various embodiments where, in one embodiment, tantalum metal is cross-rolled at 90 degrees and rectangular plate is used to make circular sputtering target disks by cutting.
Segal (U.S. Published Patent Application No. US 2002/0153071A1) relates to fabrication methods for FCC metals. Jepson (U.S. Published Patent Application No. 2002/0112789 A1), Hormann et al. (U.S. Pat. No. 4,884,746), Turner (U.S. Published Patent Application No. 2002/0125128 A1), Zhang (U.S. Pat. No. 6,193,821), and Broussoux et al. (U.S. Pat. No. 5,615,465) relate to the production of tantalum plate for sputtering targets and other uses by creating rectangular plates by various methods and then cutting a circular disk from the plate. This method can be very wasteful of expensive tantalum material.
Koenigsmann et al. (U.S. Published Patent Application No. 2003/0089429) relates to the production of tantalum sputtering targets by a powder metallurgical process. Shah et al. (U.S. Published Patent Application No. 2002/0063056 A1) relates to the production of tantalum sputtering target plate with strong (100) texture using lubricated dies and rolling in orthogonal directions. Segal (U.S. Pat. No. 6,238,494 B1) and Shah et al. (U.S. Pat. No. 6,348,139 B1) relate to the production of tantalum circular plate with strong (100) texture. In this process, circular tantalum plates are produced by a combination of forging the ingot and rolling. They reported that they needed to lubricate the dies during forging and use the lowest possible temperature for recrystallization to produce tantalum targets with strong (100) texture and suitable grain size and crystallographic texture uniformity.
In all of these methods the tantalum deformation steps are interrupted by annealing steps in order to recrystallize the tantalum to reduce the plastic strain in the metal to avoid cracking and to remove the work hardening of the metal to make the metal easier to work.
In addition, all of these methods show the transformation of the cylindrical ingot into a rectangular or square shape by forging and rolling operations and then cutting the rectangular or square plate into circles to manufacture a circular sputtering target. This conversion from circular ingot shape to rectangular shape and back to circular shape is very inefficient and wasteful of material.